Bally 5000 Plus, Manual

Page: 104 / 388

C i r cu i t Descr i pt i on ( cont ' d )
V I A
The ve r sa t l I e I n t e r f ace a d a p t e r
( V I A ) I n t e r f aces I t s p a r a l l e l I /O
por t s w i t h t he k e y pa d , t he hoppe r ,
a 5ms I n t e r r u p t , t he MPU boa r d
" T EST " but t on , a n d t he sound code
to t he b a c k p l ane s i mp l e sound or
t he sound boa r d .
Sof t wa r e c h i p s e l ec t s U29 . See
Ch i p Se l ec t I n t h i s S e c t i on .
U 1 0 p i n 1 9 sends t he l oca l I /O
s i gna l t o U7 p i n 1 8 .
U7 p i n 4 s i mu l t a neous l y sends t he
ch i p se l ec t V I A1
( CSV I A1 ) s i gna l
to :
( 1 ) U 1 0 1 p i n 1 5 .
T hen , U 1 0 1 p i n 1 7 sends a VPA
s i gna l to U 1 p i n 2 1 .
U1 p i n
1 9 sends a VMA s i gna l t o U 2 1
p i n 1 3 . U 2 1 I nv e r t s t he
s i g na l . U 2 1 p i n 1 2 sends a
VMA s i gna l t o U 29 p i n 4 .
( 2 ) U29 p i n 2 3 .
U 1 p i n 2 0 sends t he E c l ock s i gna l
t o U29 p i n 2 5 .
When U29 h a s r ece i ved t he 3 s i gna l s
a t p i n 2 3 , p i n 4 , a n d p i n 25 , U29
I s ready f o r commun i ca t i on . U29
commun i ca t e s t h r ough t he b i ­
d i r e c t i on a l d a t a bus l i ne s , DO ( p i n
33 ) t h r oug h D7 ( p i n 2 6 ) .
Sof t wa r e
add r es s e s U 2 9 t h r ough t he a d d r e s s
l i ne s , A1 ( p i n 38 ) t h r oug h A 4 ( p i n
35 ) .
U 1 p i n 9 send a R /
W
s i gn a l t o U29
p i n 2 2 .
3 . MPU BOARD
NOT E S
3-47